U.S. patent application number 11/483977 was filed with the patent office on 2008-01-10 for pressure transmitter with multiple reference pressure sensors.
Invention is credited to Mark Romo, Stanley E. Rud, John Schulte.
Application Number | 20080006094 11/483977 |
Document ID | / |
Family ID | 38543806 |
Filed Date | 2008-01-10 |
United States Patent
Application |
20080006094 |
Kind Code |
A1 |
Schulte; John ; et
al. |
January 10, 2008 |
Pressure transmitter with multiple reference pressure sensors
Abstract
Reliability and accuracy in a pressure measurement transmitter
are provided by employing a plurality of absolute or gauge pressure
sensors operating in conjunction with a differential pressure
sensor. A method is also provided to perform diagnostics based upon
the readings of the three pressure sensors. Further, should one of
the three pressure sensors fail, a reasonable estimate of process
pressure being measured by the failed sensor can be generated based
upon the remaining two sensors.
Inventors: |
Schulte; John; (Eden
Prairie, MN) ; Romo; Mark; (Eden Prairie, MN)
; Rud; Stanley E.; (Victoria, MN) |
Correspondence
Address: |
Christopher R. Christenson;WESTMAN, CHAMPLIN & KELLY, P.A.
Suite 140, 900 Second Avenue South
Minneapolis
MN
55402-3319
US
|
Family ID: |
38543806 |
Appl. No.: |
11/483977 |
Filed: |
July 10, 2006 |
Current U.S.
Class: |
73/736 |
Current CPC
Class: |
G01F 1/34 20130101; G01L
13/026 20130101; G01F 25/0061 20130101; G01L 27/007 20130101; G01M
5/0091 20130101; G01F 25/0007 20130101; G01F 23/14 20130101 |
Class at
Publication: |
73/736 |
International
Class: |
G01L 15/00 20060101
G01L015/00 |
Claims
1. A pressure transmitter comprising: a first process fluid
pressure inlet adapted to receive a first process fluid pressure; a
second process fluid pressure inlet adapted to receive a second
process fluid pressure; a differential pressure sensor coupled to
the first and second process fluid pressures; a first pressure
sensor coupled to the first process fluid pressure; a second
pressure sensor coupled to the second process fluid pressure; and
circuitry operably coupled to the first and second pressure
sensors, and coupled to the differential pressure sensor, the
circuitry configured to measure the first and second process
pressures as well as the differential pressure and provide an
indication relative to the measurements over a process
communication loop.
2. The transmitter of claim 1, wherein the first pressure sensor is
an absolute pressure sensor.
3. The transmitter of claim 2, wherein the second pressure sensor
is an absolute pressure sensor.
4. The transmitter of claim 3, and further comprising an
atmospheric pressure sensor.
5. The transmitter of claim 2, wherein the second pressure sensor
is a gage pressure sensor.
6. The transmitter of claim 1, wherein the first pressure sensor is
a gauge pressure sensor.
7. The transmitter of claim 6, wherein the second pressure sensor
is a gauge pressure sensor.
8. The transmitter of claim 7, and further comprising an absolute
pressure sensor coupled to one of the first and second process
fluid pressure inlets.
9. The transmitter of claim 1, and further comprising at least one
additional pressure sensor coupled to one of the first and second
process fluid pressures.
10. The transmitter of claim 1, wherein the circuitry includes a
power module configured to receive electrical energy from a process
communication loop to wholly power the transmitter with energy
received from the process communication loop.
11. The transmitter of claim 1, wherein the circuitry is configured
to perform at least one diagnostic function based upon signals from
the first, second and differential pressure sensors.
12. The transmitter of claim 1, wherein the first, second and
differential pressure sensors are embodied within a monolithic
sensor unit.
13. A method of operating a pressure transmitter having a first
process fluid inlet configured to receive a first process fluid
pressure and a second process fluid inlet configured to receive a
second process fluid pressure, the method comprising; measuring the
first process fluid pressure with a first pressure sensor of the
transmitter; measuring the second process fluid pressure with a
second pressure sensor of the transmitter; measuring a differential
pressure of the first and second process fluid pressures with a
differential pressure sensor of the transmitter; and determining
whether the measured differential pressure is similar to a
difference between the measured first and second fluid
pressures.
14. The method of claim 13, and further comprising determining if
the measured differential pressure is within a selected threshold
value of a difference of the first and second measured process
fluid pressures.
15. The method of claim 13, and further comprising providing an
estimate of differential pressure and an alert if the measured
differential pressure is within a selected threshold value of a
difference of the first and second measured process fluid
pressures.
16. The method of claim 13, and further comprising providing an
alarm if the measured differential pressure is not within a
selected threshold value of a difference of the first and second
measured process fluid pressures.
17. The method of claim 13, wherein the transmitter's differential
pressure process value output is a function of the differential
pressure measurement, and the measured first and second process
fluid pressures.
18. The method of claim 13, and further comprising wholly powering
the pressure transmitter with electrical energy received from a
process communication loop.
19. A method of operating a pressure transmitter having a first
process fluid inlet configured to receive a first process fluid
pressure and a second process fluid inlet configured to receive a
second process fluid pressure, the method comprising; measuring the
first process fluid pressure with a first pressure sensor of the
transmitter and determining if the first measured process fluid
pressure is valid; measuring the second process fluid pressure with
a second pressure sensor of the transmitter and determining if the
second measured process fluid pressure is valid; measuring a
differential pressure between the first and second process fluid
pressures, and determining if the differential pressure is valid;
and providing an estimate of a process fluid pressure in the event
of an invalid sensor signal as a function of at least two other
valid sensor signals.
20. The method of claim 19, and further comprising providing an
alert if any of the sensor signals is not valid.
21. The method of claim 19, wherein determining if the differential
pressure is valid includes determining if the differential pressure
exceeds a measurement range of the differential pressure
sensor.
22. The method of claim 19, and further comprising wholly powering
the pressure transmitter with electrical energy received from a
process communication loop.
23. A pressure transmitter comprising: a first process fluid
pressure inlet adapted to receive a first process fluid pressure; a
second process fluid pressure inlet adapted to receive a second
process fluid pressure; a differential pressure sensor coupled to
the first and second process fluid pressures; a first pressure
sensor coupled to the first process fluid pressure; a second
pressure sensor coupled to the second process fluid pressure; and
circuitry operably coupled to each of the first pressure sensor,
the second pressure sensor, and the differential pressure sensor,
wherein the circuitry is configured to make independent
measurements from each of at least three sensors comprising the
first pressure sensor, the second pressure sensor, and the
differential pressure sensor, and to provide an indication relative
to the measurements over a process communication loop.
Description
BACKGROUND OF THE INVENTION
[0001] In fluid process control applications in chemical, pulp,
food, and other fluid processing plants, different types of
pressure transmitters are used. These types generally include
absolute pressure transmitters that measure a process pressure
relative to a vacuum; gauge pressure transmitters that measure a
process pressure relative to local atmospheric pressure; and
differential pressure transmitters that measure a difference
between two process pressures. Pressure transmitters also typically
measure pressure over a limited range with a specified accuracy.
Typically a pressure transmitter will be manufactured in two or
more overlapping ranges, each specified to measure pressure
accurately over about a 100:1 turndown range to fill application
needs up to approximately ten thousand pounds per square inch.
[0002] Differential pressure transmitters, in particular, are
designed for specific pressure ranges and have limits as to how far
the differential pressure transmitter can be ranged down. Further,
many applications also require knowledge of the line pressure of
the monitored process. For example, commercially available devices,
such as the Model 3095 MV available from Rosemount Inc., of
Chanhassen, Minn., measures differential pressure and line pressure
in order to execute a flow calculation to provide process fluid
flow measurement. While the use of a single absolute or gauge
pressure sensor in conjunction with a differential pressure sensor
has provided advantages in the past, such devices can cease to
function if the absolute pressure sensor, or the differential
pressure sensor fails, or if any of the pressures coupled to the
pressure transmitter are outside of the selected measurement
ranges.
SUMMARY
[0003] Reliability and accuracy in a pressure measurement
transmitter are provided by employing a plurality of absolute or
gauge pressure sensors operating in conjunction with a differential
pressure sensor. A method is also provided to perform diagnostics
based upon the readings of the three or more pressure sensors.
Further, should one of the three or more pressure sensors fail, a
reasonable estimate of the output of the failed sensor can be
generated based upon the remaining sensors.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a diagrammatic view of typical process control
environment for pressure transmitters.
[0005] FIG. 2 is a block diagram of a differential pressure
transmitter in accordance with an embodiment of the present
invention.
[0006] FIG. 3 is a diagrammatic view of dual pressure transmitter
in accordance with an embodiment of the present invention.
[0007] FIG. 4 is a flow diagram of a method of operating
differential pressure transmitter having multiple absolute or gauge
pressure sensors in accordance with an embodiment of the present
invention.
[0008] FIG. 5 is a flow diagram of a method for obtaining and
reporting absolute or gauge pressure values in accordance with an
embodiment of the present invention.
DETAILED DESCRIPTION
[0009] FIG. 1 is a diagrammatic view of a typical environment for
an industrial pressure transmitter. In FIG. 1, process variable
transmitters such as flow meter 22 in process fluid line 23, level
transmitters 24, 26 on tank 28 and integral orifice flow meter in
process line 31 are shown electrically connected to control system
32. Process variable transmitters can be configured to monitor one
or more process variables associated with fluids in a process plant
such as slurries, liquids, vapors, and gasses in chemical, pulp,
petroleum, gas, pharmaceutical, food and other fluid processing
plants. The monitored process variables can include pressure,
temperature, flow, level, pH, conductivity, turbidity, density,
concentration, chemical composition or other properties of fluid. A
process variable transmitter includes one or more sensors that can
be either internal to the transmitter or external to the
transmitter, depending on the installation needs of the process
plant. Process variable transmitters generate transmitter outputs
that represent the sensed process variable. Transmitter outputs are
configured for transmission over relatively long distances to a
controller or indicator via communication busses 34. In typical
fluid processing plants, communication bus 34 can be a 4-20 mA
current loop that powers the transmitter, a FOUNDATION.TM. Fieldbus
connection, a HART (Highway Addressable Remote Transmitter)
protocol connection, or a high speed Ethernet (HSE) or a fiber
optic connection to a controller, control system or readout.
Alternatively, communication bus 34 may be implemented as a
wireless system. In transmitters powered by a process communication
loop, power must be kept low in order to comply with intrinsic
safety requirements in explosive environments.
[0010] In FIG. 1, integral orifice flow meter 30 includes pressure
transmitter 36 coupled to process communication loop or
communication bus 34. Level transmitters 24, 26 also include
pressure transmitters. Control system 32 can be programmed to
display process conditions to a human operator. Further control
system 32 and can be programmed, or otherwise configured, to sense
the process conditions and control the process via output devices
such as current to pressure converter 38 and control valve 40, for
example.
[0011] FIG. 2 is a block diagram of a pressure transmitter in
accordance with an embodiment of the present invention. Transmitter
200 includes loop communications module 202 configured to couple to
a process communication loop or bus. Loop communication module 202
generates and/or receives signals in accordance with a process
communication standard communication protocol. Loop communication
module 202 is coupled to controller 206 thereby allowing controller
206 to interact with one or more devices on the process
communication loop through module 202. Power module 204 is also
coupled to the process communication loop or bus, and receives
power and conditions, or otherwise adapts, the received power for
provision to other electrical components within the transmitter.
Power module 204 can allow the pressure transmitter to be wholly
powered from electrical energy received through the loop.
Alternatively, communication module 202 may be adapted for use
according to a wireless system and protocol.
[0012] Measurement circuitry is coupled to power module 204,
controller 206 and pressure sensors 218, 220, 222. Measurement
circuitry receives operating power from module 204 and is
configured to sense an electrical characteristic of each of sensors
218, 220 and 222 and provide an indication of the sensed
characteristic to controller 206. Measurement circuitry 208 can
include a known analog-to-digital converter. Additionally,
measurement circuitry 208 can include a multiplexer to allow
measurement circuitry 208 to couple to each of sensors 218, 220,
and 222 individually, in turn. Measurement circuitry 208 can
include any suitable circuitry or components that allow circuitry
208 to obtain measurements from sensors 218, 220 and 222. For
example, if differential pressure sensor 218 is a capacitive
pressure sensor, but absolute pressure sensors 220, 222 are
resistive strain-gauge type sensors, then measurement circuitry 208
will include suitable capacitance and resistance sensing circuitry,
as well as circuitry allowing the signals to be disambiguated from
one another, such as a multiplexer. Those skilled in the art will
recognize that embodiments of the present invention can be
practiced by employing dedicated measurement circuitry for each
sensor, or combinations thereof, and that such dedicated circuitry
can be used in place of, or in combination with, a multiplexed
configuration.
[0013] In this embodiment, absolute/gauge pressure sensor 220 is
coupled to pressure P1 applied to process fluid inlet 210 by virtue
of an isolation fluid within line 214. Similarly, absolute/gauge
pressure sensor 222 is coupled to pressure P2 applied to process
fluid inlet by virtue of isolation fluid within line 216.
Differential pressure sensor 218 is coupled to lines 214 and 216
and provides an indication of the pressure difference between lines
214 and 216 to measurement circuitry 208. Transmitter 200 can
include additional absolute or gauge pressure sensors coupled to
each of lines 214, 216. Optional sensors 230, 232 are indicated in
phantom in FIG. 2 as coupled to lines 214, 216, respectively.
Optional sensor 230, 232 may be selected to have different pressure
measurement ranges than sensors 220, 222, or they can simply
provide redundancy. Additionally, optional sensors 230, 232 can be
selected to provide additional and/or complementary functions
relative to sensors 218, 220 and 222. For example, if sensors 220
and 222 are gage sensors, one or both of optional sensors 230, 232
could be an absolute pressure sensor. Additionally, if sensors 220
and 222 are absolute pressure sensors, an optional sensor 354 could
be an atmospheric pressure sensor coupled to inlet 317 (shown in
FIG. 3). Although inlet 317 is illustrated as a wiring inlet, inlet
317 may take any suitable form, and may, in fact, be a separate
inlet than the wiring inlet.
[0014] FIG. 3 is a diagrammatic view of a pressure transmitter in
accordance with an embodiment of the present invention. Transmitter
300 includes field wiring housing 302 that surrounds wiring
compartment 304. The wiring housing 302 can be formed of a metal
such as aluminum or stainless steel, or housing 302 can be formed
of a suitable plastic. Wiring housing 302 preferably includes a
vent or inlet 317 that couples atmospheric pressure to the interior
of wiring housing 302. Preferably, mounting stand-offs 306 are
formed inside the wiring compartment 304 and a compartment cover
308 is threaded and engages corresponding threads inside the wiring
compartment as illustrated at 309. A permanently sealed transmitter
assembly 310 is threaded and engages corresponding threads inside
the wiring compartment as illustrated at 311. Transmitter assembly
310 is a pressure transmitter assembly and includes sealed isolator
diaphragms 332, differential pressure sensor 334 absolute pressure
sensors 301, 307 and one or more printed circuit boards 336.
Differential pressure sensor 334, is coupled to circuit board 336
via leads 335. Absolute or gauge pressure sensors 307, 301 are
coupled to circuit board 336 by leads 313, 305, respectively.
Isolator diaphragms 332 in the process inlets are coupled to
differential pressure sensor 334 by lines 350, 351, that are filled
with a suitable isolator fluid, such as silicone oil. Line 351 also
couples line pressure from one of the process inlets to absolute
pressure sensor 301. Similarly, line 350 also couples line pressure
from the other process inlet to absolute pressure sensor 307.
Transmitter assembly 310 has a transmitter electrical connector 312
that is accessible inside wiring compartment 304. Preferably,
transmitter assembly 310 has an outer metal housing 338 that is
permanently welded shut at weld 340 and a hermetically sealed
feedthrough 342 surrounding the transmitter electrical connector
312. Printed circuit board 336 inside transmitter assembly 310 is
thus permanently sealed and protected from the atmosphere
surrounding transmitter 300.
[0015] In this embodiment, transmitter 300 also includes an
electrical connector 314. Electrical connector 314 includes
terminals 316 that are adapted for electrical connection to field
wiring 318, which couples the pressure transmitter to a control
room, illustrated diagrammatically at 303, and/or to one or more
other field devices. Field wiring 318 typically uses long distance
signaling comprising HART serial communication over a two-wire 4-20
mA industrial control loop that energizes transmitter 300 and
provides remote electrical transmission of process fluid variables
sensed by transmitter assembly 310, but can also comprise various
known industrial busses such as FOUNDATION.TM. Fieldbus, Profibus
or other known communication protocols including wireless
communication protocols. Screw 328 can mount electrical connector
314 to mounting stand-offs 306. Electrical connector 314 can also
include sealed programming jumper assemblies 320 and sealed
programming pushbutton switches 330. Jumper assemblies 320 each
include removable jumper body 326 that can be inserted in one of
several orientations for programming. Electrical connector 314 may
also include a sealed cable 322 that terminates in a sealed plug
324 that plugs into the transmitter electrical connector 312 and
seals to the body of transmitter assembly 310.
[0016] Pressure transmitter 300 optionally includes atmospheric
pressure sensor 354 disposed within housing 302. Pressure sensor
354 senses pressure within housing 302, which is coupled to
atmospheric pressure by virtue of inlet 317. Sensor 354 may be
electrically coupled the sealed pressure transmitter assembly 310
via feedthrough 342. Thus, an indication of atmospheric pressure
can be used by circuitry on circuit board 336 to reference any
desired pressures to atmospheric pressure. Pressure sensor 354 may
be any suitable type of pressure sensor including, without
limitation, a capacitive pressure sensor, a resistive-strain gauge
pressure sensor, a piezo-resistive pressure sensor, an optical
pressure sensor, or any other suitable type of pressure sensor.
[0017] Transmitter 300 provides a pressure output over field wiring
318 and also provides indications of absolute pressure as measured
with either, or both, of absolute pressure sensors 301, 307 over
wiring 318. The line pressure output can be the sensed absolute
pressure, a calculated gauge pressure using a serial communication
signal received by transmitter 300, or both.
[0018] Circuit 336 receives an indication of differential pressure
between the process inlets and provides an indication of
differential pressure, or any suitable parameter based on the
differential pressure, over wiring 318. Absolute/gauge pressure
sensor 301 receives an indication of pressure within line 351 and
provides such indication to circuit 336. Further, absolute/gauge
pressure sensor 307 generates an indication of pressure within line
350 and provides such indication to circuit 336. Preferably each of
sensors 301 and 307 sense the same type of pressure (e.g. absolute
or gauge). Moreover, those skilled in the art will recognize that
pressure sensors 301 and 307 can be absolute pressure sensors or
gauge pressure sensors simply depending on whether they are
referenced to a vacuum, or to atmospheric pressure. Further still,
while FIG. 3 illustrates differential pressure sensor 334, and
absolute pressure sensors 301 and 307 separately, they may, in
fact, be part of one monolithic unit. Moreover, the pressure
sensors may be constructed in accordance with any suitable pressure
sensor manufacturing techniques, and may sense pressure in
accordance with known, or later developed, pressure sensing
techniques. For example, any or all of pressure sensors 334, 301
and 307 may be capacitive pressure sensors, resistive-strain gauge
pressure sensors, piezo-resistive pressure sensors, optical
pressure sensor, or any other suitable type of pressure sensor.
[0019] FIG. 4 is a flow diagram of a method of operating pressure
transmitter having multiple absolute or gauge pressure sensors in
accordance with an embodiment of the present invention. Method 400
begins at block 402 where the pressure transmitter obtains high and
low absolute pressure measurements (AP.sub.H and AP.sub.L) as well
as a differential pressure measurement. At block 404, the pressure
transmitter determines whether the measured differential pressure
is within the specified measurement range for the differential
pressure sensor. If the measure differential pressure is within the
specified range, control passes to block 406 where the pressure
transmitter determines whether the quantity AP.sub.H-AP.sub.L is
essentially equal to the measured differential pressure, within the
measurement accuracy of the absolute/gauge pressure sensors and the
differential pressure sensor. If they are essentially equal,
control passes to block 408 where the valid differential pressure
is reported and control subsequently returns to block 402 via line
410. However, if, at block 406, quantity AP.sub.H-AP.sub.L does not
equal the measured differential pressure, then control passes to
block 412 where the differential pressure transmitter determines
whether the difference between the quantity AP.sub.H-AP.sub.L and
the measured differential pressure exceeds a selected threshold. If
the threshold is exceeded, control passes to block 414 where the
differential pressure transmitter generates an alarm condition
indicating a fault. The generated alarm can be any suitable alarm
either indicated locally at the pressure transmitter, such as a
visual or audible alarm, and/or an alarm message that may be
transmitted by the differential pressure transmitter along the
process communication loop. In addition to generation of the alarm,
an option can be provided, either locally or via interaction
through a process control loop, to initiate sensor health
diagnostics to locate or identify the cause.
[0020] If the threshold is not exceeded, control passes to block
416 where the differential pressure transmitter generates a
compensated differential pressure and generates and alert
indicating that the differential pressure data being provided is a
compensated quantity. One example of compensation includes
selecting a backup value, such the quantity AP.sub.H-AP.sub.L and
providing that as the differential pressure, and then also
generating an alarm. Another example includes determining whether
the measured differential pressure is at or near a limit of its
effective measuring range, and discounting the weight of the
differential pressure sensor signal value in a weighted average
with the quantity AP.sub.H-AP.sub.L. Accordingly, as the
differential pressure sensor begins to approach or operate beyond
its specified range, the weight of its signals can be heavily
discounted such that the compensated output becomes more and more
focused upon the values provided by the absolute pressure sensors.
Yet another example, includes examining the magnitude of recent
changes of each quantity and discounting or not selecting the
quantity that has changed the most, and subsequently generating an
alarm. Thus, if one sensor should become an open circuit, the
transmitter would immediately switch to the other measurement
regime, and would generate an alarm. These are simply examples of
ways in which compensation can be provided. Certainly other
mathematical formulas and techniques are within the spirit and
scope of embodiments of the present invention.
[0021] Referring to block 404, if the measured differential
pressure is not within its range, control passes to block 418 where
the differential pressure transmitter provides an estimate of the
differential pressure as the difference between AP.sub.H and
AP.sub.L. At block 420, the estimated differential pressure is
provided and an alert, indicating that the quantity is an estimate
is provided. FIG. 4 illustrates that control from blocks 416 and
420 returns to block 402 via line 422.
[0022] FIG. 5 is a flow diagram of a method for obtaining and
reporting absolute or gauge pressure values in accordance with an
embodiment of the present invention. Method 500 begins at block 502
which is substantially equivalent to block 402 illustrated with
respect to method 400. Essentially, the pressure transmitter
obtains sensor signals from both absolute/gauge pressure sensors as
well as the differential pressure sensor. Control then passes to
block 504 which determines if the high absolute pressure sensor
signal (AP.sub.H) is valid. This may be as simple as checking to
determine if the sensor is shorted, or an open circuit. Further,
this validity check may include comparing the current sensor value
with recently acquired sensor values to determine if a significant
jump or change has occurred in the value which jump or change is
not reflected in the other two pressure sensor values. If block 504
determines that AP.sub.H is valid, control passes to block 506
where the pressure transmitter performs a similar analysis on the
low absolute/gauge pressure sensor value (AP.sub.L). If that value
is valid as well, control passes to block 508 where both
absolute/gauge pressure values are reported, or otherwise used in
calculations of the pressure transmitter. However, if one of the
absolute or gauge pressure sensors has failed, an estimate of the
failed sensor's value can be estimated. For example, at block 504,
if AP.sub.H is not valid, control passes to block 510 where an
estimate of AP.sub.H is provided as the sum of the low absolute or
gauge pressure (AP.sub.L) and the differential pressure measurement
value. Similarly, at block 506, if the low absolute or gauge
pressure sensor signal is invalid, control passes from block 506 to
block 512 where an estimate of AP.sub.L is provided as AP.sub.H
minus the differential pressure.
[0023] It is known to use line pressure to compensate for
differential pressure measurements. However, embodiments of the
present invention provide the ability to generate such compensation
even in the event that one of the absolute or gauge pressure
sensors should fail. Moreover, high level diagnostics are provided
by essentially monitoring all three values (both absolute or gauge
pressure sensor signals and the differential pressure sensor
signal) during operation. Thus, the pressure transmitter can
provide the differential pressure as well as the line pressure. The
differential pressure range covered is essentially the range
covered by the differential pressure cell and up to a differential
pressure of full line pressure on one port and zero pressure on the
other port as calculated by the difference of absolute or gauge
pressure sensors. In the event that the differential pressure
sensor and/or its associated measurement circuitry fails, the
transmitter can go into a limp mode to calculate and provide an
estimate of differential pressure as the difference between the
absolute or gauge pressure sensors. In some configurations, this
will result in a reduced accuracy differential pressure measurement
as compared to the value from the differential pressure sensor, but
could allow continued operation. However, the degree to which the
accuracy is reduced depends upon the sensor configuration used. The
pressure transmitter would also generate an alarm or alert to the
control system or a technician indicative of the failure. In the
event that one of the absolute or gauge pressure sensors fail, the
transmitter can also go into limp mode and that value can be
estimated, as set forth above, based upon the remaining absolute or
gauge pressure sensor signal and the differential pressure sensor
signal. Again, alarms or alerts would indicate such limp mode to
the control system or a technician.
[0024] Although the present invention has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes may be made in form and detail without
departing from the spirit and scope of the invention. For example,
although the present invention has been described primarily with
respect to a pair of absolute or gauge pressure sensors used in
conjunction with a single differential pressure sensor, additional
absolute or gauge pressure sensors can also be used to increase the
effective measurement range of such absolute or gauge
measurements.
* * * * *